Direct use of acoustic power in stirling engine for heat removal

ABSTRACT

A Stirling engine includes a piston and a displacer that move in phased reciprocating motion within one or more cylinders. A working fluid is contained within the one or more cylinders, and a position of the displacer causes the working fluid to be in contact with either a hot heat exchanger or a cold heat exchanger. A volume of the working fluid governed by a position of the piston is referred to as a compression space. The piston, the displacer and the working fluid operate in a thermodynamic cycle that generates acoustic wave power. An acoustic pump is driven by the acoustic wave power.

FIELD OF THE INVENTION

The present invention relates generally to Stirling engines, and particularly to utilizing acoustic power in such an engine for heat removal.

BACKGROUND OF THE INVENTION

The Stirling cycle is a well-known four-part thermodynamic process, typically operating on a gas, to produce work, or conversely to effect heating or refrigeration. The four parts, shown in FIG. 1, are isothermal expansion, isochoric heat extraction, isothermal compression, and isochoric heat addition. The process is closed, in that the gas remains within the system performing the cycle at all times during the cycle.

A typical Stirling engine has pistons that respond to the heating/expansion and cooling/contraction of a contained gas as part of the Stirling cycle. The motion of the pistons may provide available work. A regenerative heat exchanger or regenerator increases the engine's thermal efficiency. FIG. 1 shows a Stirling cycle having such a regenerator between two heat exchangers, a cold side (cold sink) heat exchanger and a hot side heat exchanger.

It is noted that thermoacoustic Stirling heat engines are another group of devices utilizing a Stirling thermodynamic cycle. These devices share some fundamental physical properties with Stirling engines, namely a contained gas which approximates a Stirling cycle in the regenerator. However, a thermoacoustic engine differs from a Stirling engine in that it has no displacer, such as typically found in a Stirling engine.

In a typical Stirling engine, in order to remove the heat from the cold sink heat exchanger, an electric pump is generally used to pump a liquid through a chiller, radiator or other cooling apparatus. However, by using this configuration there is an inherent increased power loss, since the engine is using some of its end product (electricity) for its continuous operation.

SUMMARY OF THE INVENTION

The present invention seeks to provide a novel method for cooling Stirling engines, wherein the acoustic power produced by the engine is used for heat removal, as is explained more in detail hereinbelow. This improves the efficiency of the engine. Acoustic power is generated by the thermodynamic cycle gain. In the present invention, it is extracted to drive a piston, acoustic pump, and the like.

The acoustic power is directly applied into the cooling loop circulation system in a Stirling engine. For example, the acoustic power is used in an acoustic pump to pump liquid through a cooling device, such as a chiller, radiator or others. This eliminates the inefficient transformation of acoustic work into electricity and then transformation of the electricity into pumping work.

It is noted that the term “compliance volume” refers to any practically available ambient volume.

There is thus provided in accordance with a non-limiting embodiment of the invention a Stirling engine including a piston and a displacer that move in phased reciprocating motion within one or more cylinders, a working fluid contained within the one or more cylinders, wherein a position of the displacer causes the working fluid to be in contact with either a hot heat exchanger or a cold heat exchanger, and wherein a volume of the working fluid governed by a position of the piston is referred to as a compression space, the piston, the displacer and the working fluid operating in a thermodynamic cycle including a first phase wherein the piston compresses the working fluid in the compression space, a second phase wherein the working fluid is displaced from the cold heat exchanger to the hot heat exchanger and a pressure of the working fluid increases, a third phase wherein a volume of the compression space increases as heat is drawn in from outside the engine, and a fourth phase wherein the working fluid is transferred from the hot heat exchanger to the cold heat exchanger, the thermodynamic cycle generating acoustic wave power, and an acoustic pump driven by the acoustic wave power.

The acoustic pump may pump and circulate cooling liquid for the cold heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

FIG. 1 is a simplified illustration of a prior art Stirling cycle; and

FIG. 2 is a simplified block diagram of a Stirling engine utilizing acoustic power for heat removal, constructed and operative in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIG. 2, which illustrates a block diagram of Stirling engine 10, constructed and operative in accordance with a non-limiting embodiment of the present invention.

As in a typical Stirling engine, the Stirling engine 10 has a piston 12 and a displacer 14 that move in phased reciprocating motion within cylinders 16 which, in some embodiments of the Stirling engine, may be a single cylinder. A working fluid 15 contained within cylinders 16 is constrained by seals from escaping around piston 12 and displacer 14. The working fluid 15 is chosen for its thermodynamic properties, e.g., helium at a pressure of several atmospheres. The position of displacer 14 governs whether working fluid 15 is in contact with a hot interface (or hot heat exchanger) 18 or a cold interface (or cold heat exchanger) 20, corresponding respectively to the interfaces at which heat is supplied to and extracted from working fluid 15. The volume of working fluid 15 governed by the position of the piston 12 is referred to as compression space 22.

As in many Stirling engines, a load, such as an alternator (having alternative back space 25), may be connected to the piston 12 inside or outside the casing.

During the first phase of the engine cycle, piston 12 compresses fluid 15 in compression space 22. The compression occurs at a substantially constant temperature because heat is extracted from the fluid to the ambient environment.

During the second phase of the cycle, displacer 14 moves in the direction of cold heat exchanger 20, with the working fluid 15 displaced from the region of cold heat exchanger 20 to the region of hot heat exchanger 18. At the end of this transfer phase, the fluid 15 is at a higher pressure since it has been heated at constant volume.

During the third phase (the expansion stroke) of the engine cycle, the volume of compression space 22 increases as heat is drawn in from outside engine 10, thereby converting heat to work. At the end of the expansion phase, compression space 22 is full of cold fluid 15.

During the fourth phase of the engine cycle, fluid 15 is transferred from the region of hot heat exchanger 18 to the region of cold heat exchanger 20 at constant volume by motion of displacer 14 in the opposing sense. At the end of this second transfer phase, fluid 15 fills compression space 22 and cold heat exchanger 20, and is ready for a repetition of the compression phase.

Additionally, upon passing from the region of hot heat exchanger 18 to the region of cold heat exchanger 20, fluid 15 passes through a regenerator 24. Regenerator 24 absorbs heat from fluid 15 when it enters hot from the region of hot heat exchanger 18, and heats fluid 15 when it passes from the region of cold heat exchanger 20.

The complete thermodynamic cycle generates acoustic wave power. In accordance with an embodiment of the invention, an acoustic pump 26 is connected to compression space 22, alternator back space 25, or a compliance volume 27, and receives the acoustic wave power generated there. This acoustic wave power drives acoustic pump 26, which pumps and circulates cooling liquid for the cold heat exchanger 20. Accordingly, the invention takes advantage of the available acoustical work without transforming it first into electricity in order to pump cooling liquid.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art. 

What is claimed is:
 1. A Stirling engine comprising: a piston and a displacer that move in phased reciprocating motion within one or more cylinders; a working fluid contained within said one or more cylinders, wherein a position of said displacer causes said working fluid to be in contact with either a hot heat exchanger or a cold heat exchanger, and wherein a volume of said working fluid governed by a position of said piston is referred to as a compression space; said piston, said displacer and said working fluid operating in a thermodynamic cycle comprising a first phase wherein said piston compresses said working fluid in said compression space, a second phase wherein said working fluid is displaced from said cold heat exchanger to said hot heat exchanger and a pressure of said working fluid increases, a third phase wherein a volume of said compression space increases as heat is drawn in from outside said engine, and a fourth phase wherein said working fluid is transferred from said hot heat exchanger to said cold heat exchanger, the thermodynamic cycle generating acoustic wave power; and an acoustic pump driven by said acoustic wave power.
 2. The Stirling engine according to claim 1, wherein said acoustic pump is connected to said compression space.
 3. The Stirling engine according to claim 1, wherein said acoustic pump is connected to an alternator back space in operational connection with said piston.
 4. The Stirling engine according to claim 1, wherein said acoustic pump is connected to a compliance volume.
 5. The Stirling engine according to claim 1, wherein said acoustic pump pumps and circulates cooling liquid for said cold heat exchanger. 